Once you have made a hydrogen or hot air balloon rise up into the air the obvious next step is to put some sort of propulsion system into it so you can go where you want to go, not where the wind blows you. Some American publications give balloons with some sort of propulsion system grand titles such as self-propelled lighter than air craft, but the common name is airship, and this is the name that I shall use. Correctly, both heavier-than-air and lighter-than-air flying machines are aircraft, so I shall use the word aeroplane rather than aircraft for heavier-than-air flying machines.
The first Manned balloon flight was made in November 1783, but it was a hundred years before all the problems of building an airship were finally overcome.
I have provided a few Notes at the end of this Page: these are mainly for teachers and may safely be ignored by other people. Notes are shown thus(1).
Although the first ever Manned balloon flight was in a hot air balloon, the first Manned flight in a hydrogen balloon was made only a month later, and the problems of providing a safe, reliable and controllable supply of hot air were so great that after about 1800 almost all balloons were filled with hydrogen. Hot air ballooning was not revived until the development of the lightweight propane burner in the 1960s. During the 19th century hydrogen was used in all balloons and airships, but during the 20th century hydrogen was progressively replaced by helium which, although it does not give as much buoyancy as hydrogen and is much more expensive, is not inflammable and so is considered safer. For the rest of this Page I use the word gas to mean either hydrogen or helium.
In the very earliest days of ballooning there were a few attempts to make a hot air airship but these led nowhere because of the lack of a safe and reliable source of hot air, and so are not considered on this Web Page. But today there is a renewed interest in hot air airships. They are however considered only on the Page on 21st Century Airships because by the time the first modern hot air airship was built all the technical problems associated with the development of the airship had been overcome: hot air airships played no part at all in the development of the airship in the 19th and 20th centuries.
The easiest shape to make a balloon is spherical. A sphere also has the lowest surface area for a given volume, so a spherical balloon needs less material for the envelope, and so weighs less, than any other shape. However a spherical balloon has a very high air resistance, so it is very difficult and very energy-inefficient to make it go in any direction other than the direction of the wind. An elliptical or cigar-shape gives much less air resistance, and as a result almost every airship that has ever flown has been approximately one of these shapes.
There are three basic types of airship.
Non-rigid airships consist of a large bag (envelope) containing the gas (hydrogen or helium), with a gondola suspended from it. The shape of the envelope is maintained by the pressure of the gas inside it, in exactly the same way that a party balloon keeps its shape because of the pressure of the air inside it. Non-rigid balloons are in fact quite rigid: a better description would be pressure-rigid, but the term non-rigid is here to stay.
If you have an approximately spherical party balloon it is very difficult to twist or bend it into another shape, but a long thin balloon is very easily made into another shape - even a hat-shape!
Non-rigid airships are often called blimps: this term originated on 5th December 1915 when an American Naval Officer by the name of A D Cunningham tapped the side of a United States Navy non-rigid airship and mimicked the blimp sound it made. It is not often we can be this certain about how and when a word was first used!
Using the materials and techniques available before the end of the 19th century the maximum size of a non-rigid airship before it would lose its shape was a lot less than 100 m, and also the engine and the materials from which the envelope and gondola were made were much heavier, so 19th century non-rigid airships could only carry a very few people. Henri Giffard's 1852 airship, described in another Section, was 44 m long but could still carry only one person - but he also built a spherical balloon which carried twenty people!
As the only way in which a balloon or airship can carry a bigger load is to make it bigger the next stage in the development of the airship was to give it a rigid wooden keel. This allowed the envelope to be made much longer without losing its shape. Airships built with a keel in this way are called semi-rigid. However the fully rigid airship, described next, was so much more efficient than the semi-rigid airship that only a few semi-rigid airships were built. But it was an Italian semi-rigid airship, the 106 m long Norge, which flew over the North Pole from Norway to Alaska, the first flight over the North Pole.
Although aluminium is the commonest metal in the Earth's crust it is also one of the most difficult metals to separate from its ores. It was first separated in 1825 by the Danish scientist Hans Christian Oersted (1777 - 1851), but the method used was very difficult and expensive, and for the next sixty years aluminium was little more than a curiosity for the very rich. Then in 1886 two young men, Charles Hall in America and Paul-Louis-Toussaint Heroult in France, independently developed a much simpler and cheaper method of extracting aluminium. This is usually called the Hall process although it was agreed that patents would be given to both Hall and Heroult.
Aluminium was first extracted from a mineral called alumina and so was originally named aluminum (without the second i). It was officially renamed aluminium to bring the name into line with other metals such as sodium, potassium, calcium, magnesium etc. But it is still called aluminum in the United States.
It was the discovery of the Hall process which made the next stage in the development of the airship possible. A rigid airship originally had an aluminium framework, although today other materials such as carbon fibre (graphite) are also used. The gas is contained in bags (gas bags) which are enclosed inside this framework, and then the whole airship is covered with a fabric envelope. This rigid framework makes it possible to build airships much longer than 100 m.
Aluminium was the first material strong enough and light enough to make a rigid airship.The gas bags do not take up all of the space inside the frame: there is also room for fuel and other materials, and walk-ways to allow access to every part of the airship in flight. The gondola housing the passengers and crew of a rigid airship was originally attached to the frame rather than suspended from the envelope; on the Hindenburg (described below) the crew and passenger compartments were integrated into the frame. Rigid airships are usually cigar-shaped rather than elliptical because this means that all the frames in the middle section can be of a standard size and design, regardless of the length of the airship and the type of gondola: this makes it much cheaper and easier to develop and build airships of different lengths and for different purposes. Because all Zeppelin airships were cigar-shaped many books say that all airships are cigar-shaped, even though a quick look at any modern non-rigid airship will show that this is not true.
The World's first aluminium-framed rigid airship was built by a Croatian engineer called David Schwarz (1852 - 1897). It was powered by a 10 kW Daimler petrol engine and was 38 m long. Unfortunately Schwarz died just before its first and only flight. This flight was in Berlin, on 3rd November 1897. Seven minutes into what had until then been a very successful flight a belt driving one of the four propellers broke, the pilot lost control and panicked and started letting out hydrogen, and the airship crashed. Count von Zeppelin had offered to co-operate with Schwarz but his offer had been turned down.
The next rigid airship was built by Count Ferdinand von Zeppelin (1838 - 1917). It made its first flight on 2nd July 1900. He called it the LZ 1, for Luftschiff Zeppelin (Zeppelin airship). It was cigar shaped, 128 m long and 12 m in diameter, and powered by two 11 kW Daimler engines. You can read about and see some photographs of its first flight by visiting the First Zeppelin web site.
The Zeppelin Airship Company went on to build very many more rigid airships. Perhaps the best known (for all the wrong reasons) is the LZ 129, the Hindenburg, built in 1936, although the most successful was the LZ 127, the Graf Zeppelin. You can read about the crash of the Hindenburg on another Page of my Web Site.Another German Company, Luftschiffbau Schütte-Lanz, started to build rigid airships in 1909, and by 1917 had built about twenty. Some of these were used against Britain during the First World War. In many ways they were more advanced than Zeppelins, but they had glued wooden frames which tended to come unstuck in damp conditions. To help the German war effort most of the more advanced features of the Schütte-Lanz airships were also incorporated into the Zeppelins, and no more Schütte-Lanz airships were built after the end of the War.
Many trade names, like Sellotape, Hoover, Thermos, Hovercraft, Coke etc, have passed into common use. The word Zeppelin is a trade name for airships built by the Zeppelin Airship Company, but has often been used for any large or rigid airship. In particular the British have always used the word Zeppelin for all German airships of the First World War.
In the same way, during the 1920s and 1930s any large passenger aeroplane was commonly known as a Handley Page, and today all non-rigid airships are often called Goodyears.
France was the first country to fly a balloon and build an airship, and was very much involved in the development of balloons and airships, and also aeroplanes. For this reason many words associated with balloons, airships and aeroplanes (even the word aeroplane) are French. The word dirigible is the French for steerable, and originally meant any balloon or airship which could be steered. But it later came to be applied only to rigid airships, and then all rigid airships became known as dirigibles. Today it is not often used in this way except in France but you may still find the word in older books.
A rigid airship is much more expensive and difficult to make than a non-rigid airship, so it really comes into its own only for lengths too great for a non-rigid one - this is about 100 m. Schwarz’s airship, at 38 m long, was really too short to have any advantage over a non-rigid; however beyond 100 m the sky’s the limit (forgive the pun) for a rigid airship: the Hindenburg was 245 m long and, after taking off the weight of the engines, framework, envelope and gas bags etc, still had enough lift to carry seventy two passengers in a passenger compartment weighing more than 200 tonnes - enough for a separate smoking room (in a hydrogen-filled airship!), twin-berthed cabins for sleeping, and a grand piano!
To propel an airship through the air you need some sort of power source and some way of applying it. At the end of the eighteenth century the only available power sources were horsepower, steampower and Manpower. Various ways of applying these were used: oars, paddles and flapping wings among them, but the only way which worked was the airscrew (propeller). James Watt (1736 - 1819) had fitted a propeller to a steam engine in 1770, although the idea of the airscrew goes back to the time of the Ancient Egyptians, and Leonardo da Vinci (1452 - 1519) had designed a flying machine fitted with an airscrew. So simple but very inefficient airscrews were available to the early airship makers; the first really efficient airscrew was not developed until 1904, by the Wright brothers.
In 1850 a French clockmaker called Pierre Jullien demonstrated a model airship 15 m long powered by two clockwork motors. A French engineer called Henri Giffard (1825 - 1882) saw these flights, and went on to build his own, Manned, airship. This was a non-rigid airship 44 m long and powered by a 2.2 kW steam engine. On 24th September 1852 he travelled 27 km at a speed of 10 km/hour. You can see a picture of his airship on the Henri Giffard web site.
From time immemorial Man has dreamed of flying, but almost all of these dreams have been about flying on wings, like birds. During the 19th century a lot of work was being done on heavier-than-air flying machines (aeroplanes) and by the time Giffard built his airship most scientists and engineers had become more interested in aeroplanes than airships. (Unfortunately these very exciting times are outside the scope of this Web Page, but there are plenty of other sites dealing with it: try a Google search on George Cayley as a starting point.) So it was not until 1872 that a French engineer called Dupoy de Lome built the next airship, almost identical to Giffard’s except that it was powered by four men working a windlass. Then in 1883 two French brothers Gaston and Albert Tissandier built another airship, still based on Giffard’s design, this time powered by an electric motor and a (very heavy) battery. Neither of these were any better than Giffard’s 1852 airship because the propulsion systems were no more powerful and weighed just as much.
In 1884 Charles Renard and Arthur Krebs, two officers in the French Army Corps of Engineers, built a much improved non-rigid airship. They called it La France. It was 50 m long and was powered by a 6.3 kW electric motor. But they used a special light-weight battery. This gave it a top speed of about 14 km/hour but an endurance of only about 30 minutes and a range of only about 8 km. Over the next two years it made a number of flights in different weather conditions. In spite of its very limited range and endurance it was the World’s first Manned flying machine capable of repeated sustained fully controlled flight.
But the Age of The Airship really became possible in 1883, when Gottlieb Daimler (1834 - 1900) built the World's first four-stroke petrol internal combustion engine. In an internal combustion engine the fuel is burnt inside the engine rather than outside it as in a steam engine. This makes it very much smaller and lighter. The Brazilian Alberto Santos-Dumont (1873 - 1932) was the first person to put a petrol engine into a true Manned airship; the American aviation pioneer T S C Lowe had put a petrol engine into a balloon in 1889, but used it only to provide control during take-off and landing - this is described in the next Section. Santos-Dumont was born in Brazil of very rich parents. His family came to Paris in 1891. At the end of the 19th century Paris was the centre of the aviation world. Santos-Dumont began experimenting first with balloons and then with non-rigid airships. His Number 1 Airship made its first flight in Paris on 18th September 1898, and he went on to build fourteen more. In his Number 9 Airship (which he called his Runabout) he would fly along the streets of Paris, even stopping for lunch at an open-air café!
As an aside, if anyone knows of a book or web site which gives the length of any of Santos-Dumont’s airships please could they e-mail me so I can include them here: they would be very interesting but I cannot find them anywhere.
Two years after Santos-Dumont’s Number 1 Airship made its first flight the first Zeppelin rigid airship made its first flight, and this was powered by two petrol engines. From then on almost all airships have been powered by petrol or diesel engines.
Unlike Count von Zeppelin however Santos-Dumont soon lost interest in airships and devoted the rest of his life to heavier-than-air flying machines: on 23rd October 1906 he became the first person to make an officially observed sustained and fully-controlled flight in an aeroplane in Europe. He wrote a fascinating book about his work on flying machines. Many people regard him as one of the greatest figures in aviation history.
At sea level atmospheric pressure is about 1013 mb and the density of the air is about 1.22 kg/m3, whereas the density of helium(4) is only about 0.18 kg/m3, a difference of 1.04 kg/m3. This means that at sea level 1000 m3 of helium will lift about 1.04 tonnes. But at an altitude of 3000 m atmospheric pressure is only about 701 mb, the density of the air is only 0.91 kg/m3 and the density of helium is only about 0.13 kg/m3, a difference of 0.78 kg/m3, and of course at higher altitudes the difference is even less. So at an altitude of 3000 m a balloon or airship containing 10 000 m3 of helium will lift a total weight (including the envelope) of 7800 kg. At this height our balloon will be neutrally buoyant: the buoyancy of the balloon is exactly equal to its weight. But because the density of the air changes with height, at any other height the balloon will not be neutrally buoyant: if it were to go higher its weight would be greater than its buoyancy, but if it were to go lower its buoyancy would be greater than its weight. If we want to make it go higher or lower we must change either the weight of the balloon or the volume of the helium, or both.
A balloon travels at the speed of the wind in the direction of the wind. Because of this, it is very unlikely that the place where you eventually end one balloon journey will be exactly the place where you want to start another one - not even if your name is Richard Branson and you have just flown round the world! So you will have to let all the gas out of your balloon so it can be folded up to load into the car or truck to take it away. (This is why helium ballooning is so expensive and has been replaced by hot air ballooning: all the helium is lost at the end of every flight.) Controlling the height of a helium balloon is therefore quite simple: you carry ballast in the form of bags of sand. If you want to go up you reduce the weight of the balloon by throwing out some sand and if you want to go down you reduce the volume of the helium by letting some out. You can afford to do this because all the helium is going to be lost at the end of the flight in any case.
But the place where an airship ends one journey will almost always be the place where it starts its next journey. This means that you must find a way of controlling its height without letting out (venting) any helium. Amazingly, the air-filled balloonet which enables this to be done was invented in 1783, within a few weeks of the first Manned flight in a hydrogen balloon, by Jean-Baptiste-Marie Meusmier(5), although it was not actually used in a balloon or airship for more than a hundred years.
Like many words associated with balloons and airships balloonet is a French word and is pronounced “balonay” in the French way: bal as in balance, on as in on your bike, and ay to rhyme with day.
If our airship weighs 7800 kg and is designed to operate at a maximum height of 3000 m it will need an envelope big enough to hold 10 000 m3 of helium. But at any lower altitude the amount of helium needed to provide the same buoyancy is less and so will not maintain the shape of the envelope - at sea level only 7500 m3 will be needed. So special airbags called balloonets are put inside the envelope. These can be inflated with air to compensate for the change in the volume of helium needed with altitude, so maintaining the shape of the envelope and keeping the buoyancy constant.
The first person to use balloonets in this way was the American inventor and aviation pioneer T S C Lowe (1832 - 1913). His first airship, the LPA 1 (for Lowe Planet Airship) made its first flight on 2nd August 1889. It was basically a spherical balloon with a small boat suspended from it, and was fitted with a 4.5 kW petrol engine. It was not a true airship in the way that Santos-Dumont’s airships were because his engine was so unreliable and used so much petrol that he only used it to control the balloon while taking off and landing. He controlled its height by venting gas or discharging ballast, as was usual for a balloon. He made several more flights, and then on 17th November 1889 he attempted to fly across the United States, from the Pacific coast to the Atlantic coast, taking advantage of the high altitude Westerly winds which he had earlier discovered. He reached a height of more than 5500 m, far higher than he had intended, but without balloonets to compensate for the lower pressure the balloon was damaged as the helium expanded, and also the engine froze up. He had to do an emergency landing but he could not start the engine to control the balloon as it came down and it crashed and was destroyed. Fortunately he was not seriously injured. His next airship, the LPA 2 (also called the Pasadena) had an elliptical envelope and two engines, but, more importantly, was fitted with balloonets. It made its first flight on 17th June 1890 but was destroyed in a crash soon afterwards. Like his LPA 1 it was not a true airship. Lowe went on to build several more airships, including some true airships, and even started his own airline! You can read more about these by visiting the T S C Lowe web site.
Santos-Dumont and Count von Zeppelin, and all airship builders after them, used balloonets on all their airships.
Rigid airships need balloonets to compensate for the effects of the change of pressure with altitude on buoyancy, but not to maintain the shape of the envelope.
It is important to understand that the balloonets are there to adjust for the effects of the change of pressure with altitude, not to compensate for any changes in the weight of the airship. It is essential that the weight of the airship does not change in flight, for example as the fuel is used up, otherwise the only way to prevent the airship from gaining altitude would be to vent helium. The Graf Zeppelin (LZ 127) used a special gas fuel (Blau gaz, after its inventor Dr Hermann Blau), very similar to propane but with exactly the same density as air, which was stored in huge bags inside the envelope. This meant that as it was used up air took its place and there was no change in weight. Most other 20th century airships, including the Hindenburg, used ordinary petrol or diesel fuel and condensing engines, where the water produced by burning the fuel was condensed and stored on board to compensate for the weight of the fuel as it was burned. On the ground, loading and unloading an airship also needs to be carefully planned: for example, if an airship has been carrying a 60 tonne tank, merely driving the tank off would change the weight of the airship but not its buoyancy and it would take off like a rocket - a rocket going up sideways! Originally the weight was kept constant during loading and unloading by the use of water or sand as ballast - on some old newsreel films showing passengers boarding the Graf Zeppelin or Hindenburg, in the background you can see the ground staff taking sandbags off a special platform on the gondola as each passenger boards. Similarly, on the films of the Hindenburg disaster, at one point you can see water pouring down out of the airship: this is probably the water ballast being released as the structure breaks up - the airship had not had a full load of passengers on the journey from Germany and so it would have been carrying a lot of ballast. Today other methods are being developed to make it possible to operate airships from unprepared landing strips without having to take on or release ballast.
The maximum height an airship equipped with balloonets can go up to is the height at which the balloonets are empty. If our airship is designed to carry 7800 kg to a height of 3000 m, we can only make it go higher by making it carry less load. At sea level we put in less helium, and therefore more air in the balloonets. Similarly if we want it to carry a bigger load we put in more helium and therefore less air in the balloonets, so it will not go as high.Balloonets work well for altitudes up to about 5000 m. Airships designed to operate at very high altitudes, up to 30 000 m, are considered on the Page on 21st century airships.
For thousands of years small boats, even not-so-small boats, have been steered by means of a piece of wood put into the water over one side. This piece of wood has been called many things, including a steering oar and a steerboard. Because most helmsmen were right-handed the steerboard was put over the right-hand side of the boat (facing forwards). When the boat came into a harbour the steerboard would need to be on the side of the boat away from the quay, not on the port side. Today of course aircraft carriers, supertankers and cruise liners are no longer steered by the helmsman sticking a piece of wood into the water over the side of the ship, but the sides are still called port and starboard.
From the start many different ways were used to try to control the direction of a balloon, including a steering oar, but none of them worked. Sticking an oar out of one side of the basket of a balloon being blown along by the wind would, at best, just cause the balloon to spin round, like a weathercock, not change its direction of motion.
Giffard's airship was fitted with what is recognisably a rudder, and this worked quite well when the airship was moving forwards in calm air, but not in even the lightest breeze, when it flew in a circle, or when the airship was not moving. Unfortunately because up till then most attempts to steer balloons had been done with oars, many contemporary accounts of Giffard's airship refer to the rudder as an oar, and this has often caused confusion.
All later airships were fitted with rudders, initially on the gondola but later, on rigid airships, on the back end of the envelope.A rudder works well when an airship is moving but not when it is stationary. Airships such as the Hindenburg needed a large number of people holding onto ropes to control them when they were on the ground. A 21st century airship is controlled not by rudders but by swivelling the main propulsion engines or by small pivoting electric thruster motors at the front and back. These give full control of the airship even when it is hovering, and greatly reduce the number of ground handling staff needed.
Note 1 These Notes are intended primarily for science teachers and those with some prior knowledge of airships.
Note 2 I am well aware that buoyancy and weight are forces and so should correctly be expressed in newtons, but the purpose and target audience of this Web Page are such that it does not appear to me to be particularly helpful to do so when every other book and web site I have come across on the subject of airships uses kilograms or equivalent non-metric units.
Note 3 Not Used
Note 4 In this Section I have based my calculations on helium as the lifting agent because all 21st century balloons and airships use helium, although of course all the airship and balloon pioneers used hydrogen.Note 5 Meusmier's drawings show a hydrogen balloon although in his writings he refers to a Montgolfier - but as described on another Page of this Web Site it was very common in late 18th and early 19th century France to refer to all balloons as Montgolfiers, and this has caused confusion, particularly when French texts are translated into other languages.
Note 6 Throught this Page I have given the size of airships in terms of their length in metres rather than the volume of helium they contain in cubic metres, which is the more normal measurement of the size of an airship, as I think their length gives most people a better idea of their huge size.